This invention relates to metal box-like enclosures for electrical switching apparatus. More particularly, the invention relates to enclosures of the aforementioned type having a hinged door which is securely latched in the closed position by a known latching and interlock mechanism commonly referred to as a "Thomas" interlock or "Detroit" interlock.
Enclosures of the aforementioned type are used for combination starters and similar apparatus to house a circuit protective switching device and an electromagnetically operated switching contactor for controlling the operation of an electric motor. The enclosure has an external operator for manually controlling the operation of the internally housed switching apparatus. The operator, switching apparatus and a door of the enclosure are interlocked to require the enclosure door to be securely latched before the switching apparatus may be operated. Although not a part of this invention, defeater mechanisms are provided to enable a person knowledgeable in the operation of such apparatus to open the door when the switching apparatus is in an ON condition and/or to operate the switching apparatus to an ON condition when the door is open. U.S. Pat. Nos. 2,946,865,3,055,996 and 3,229,056 are examples of enclosures of the aforementioned type.
Certain applications for enclosures of the aforementioned type require the door and case to be sealed by a gasket to prohibit the entrance of impurities such as dust or moisture. However, such gasketed construction also seals the enclosure to prevent exhaustion of pressurized gas generated within the enclosure when the switching apparatus is operated under fault current conditions. This situation can cause severe damage to the enclosure and potential danger to a human operator of the apparatus.
U.S. Pat. No. 4,194,100 discloses a circuit breaker enclosure having a hinged gasketed door, an external operator handle and spring biased external latches for the door. The door is permitted limited opening against the bias of the springs to permit pressurized gas to be exhausted without damaging the enclosure. However, the resilient latching of this patent would not have utility on an enclosure having a "Detroit" or "Thomas" interlock mechanism since such mechanism is intended to securely latch the door closed with a camming action.
U.S. Pat, Nos. 4,293,153 and 4,261,189 disclose latch assemblies for the door of an electric panelboard for circuit breakers. U.S. Pat. No. 4,293,153 incorporates a spring in the door pull assembly to permit limited opening of the door upon gas pressure buildup. U.S. Pat. No. 4,261,189 incorporates a pivoted retainer plate with a handle/lock assembly to permit limited opening of the door upon gas pressure buildup. In each instance, the panelboard door is not provided with a separate latching and interlock mechanism for securely holding the door closed.